Electron beam convergence apparatus



July 16, 1968 G. K. sl-:DELwl-:CK 3,393,343

ELECTRON BEAM CONVERGENCE APPARATUS United States Patent O 3,393,343 ELECTRON BEAM CONV ERGENCE APPARATUS Gene Karl Sendelweck, Indianapolis, Ind., assignor to Radio Corporation of America, a corporation of Delaware Filed Feb. 14, 1966, Ser. No. 527,190 7 Claims. (Cl. 315-13) This invention relates to color image display Systems and particularly to improvements of means for making a plurality of electron beams of a multiple beam display device converge at all scanned points on the target electrode of said device.

An illustrative example of such a multiple beam display device is a color picture tube. Color picture tubes of the shadow mask type normally have three electron guns positioned in the neck of the tube and a target electrode including an apertured shadow mask located between the electron guns and a luminescent screen of phosphor dots. The dots are arranged in groups of three in register with respective apertures of the mask. Static magnetic means are provided for making the three electron beams converge at the center of the scanned area of the target electrode. The three beams, after passing through the shadow mask, respectively strike three phosphor dots, each emitting light of a different color. All three beams are delected by a common horizontal and vertical deflection system so that the beams systematically Scan the picture tube target.

The more the three beams are deilected from the center of the target, unless corrective measures are taken, the greater may be the misconvergence of the beams when they reach the shadow mask. It is, therefore, customary to provide dynamic electromagnetic means for correcting the misconvergence of the beams as a function of the angular deection of the beams from the center of the picture tube target. For this purpose, current waveforms of generally parabolic shape are produced from energy derived from the horizontal and vertical dellection circuits and are employed, in conjunction with three convergence electromagnets, to dynamically converage the three beams at all points of the entire scanned area of the picture tube target.

Not only must the waveforms employed have proper shapes and amplitudes in order to achieve good convergence of the three beams at all points of the picture tube target, but also the controls for the waveforms should have sulllcient ranges to enable proper adjustments so as to achieve the desired results. In a widely used energizing circuit for the beam convergence electromagnets, the windings of the red and green beam convergence electromagnets are connected in series to a relatively high voltage point of a source of parabolic wave energy and the blue beam electromagnet is connected to a relatively low voltage point of the same wave source. As a consequence, the parabolic wave amplitude control for the blue electromagnet may not have as much adjustment flexibility as desired in some instances.

It therefore, is an object of this invention to provide an improved circuit arrangement, whereby to provide greater flexibility for the control apparatus to adjust the energizing wave for a beam convergence electromagnet.

The circuit arrangement in accordance with the invention includes two sources of generally Similar voltage waves of the same polarity, the rst of which has a given maximum magnitude and the second of which has a magnitude less than said maximum amplitude. The winding of the convergence electromagnet is coupled between the two wave sources and control means are provided to vary the magnitude of the wave derived from the rst source from its maximum magnitude to one which is less than 3,393,343 Patented July 16, 1968 ICC the magnitude of the wave derived from the second source, hereby to effect a reversal of current flow in the electromagnet winding, thus increasing the adjustment flexibility of the control means.

For a better understanding of the invention, reference now will be made to the following detailed description taken in connection with the accompanying drawings, in which:

FIGURE l is a block diagram of a color television receiver in which the present invention may be embodied;

FIGURE 2 is a fragmentary sectional view of the neck portion of a color picture tube, showing the relationship of the convergence electromagnets and the electron beams controlled thereby; and

FIGURE 3 is a schematic circuit diagram of apparatus embodying the invention for controlling the convergence electromagnets at the vertical dellection frequency.

Reference rst is made to FIGURE l for a general description of a color television receiver embodying the present invention. Radiated signals received by the antenna 11 are processed in the TV receiver circuits 12 in a known manner to produce 1) video signals representing three component colors of an image to be reproduced and (2) synchronizing signals for controlling beam deflection and for other purposes such as the production of suitable signals by which to effect convergence of the three electron beams at the target electrode of the image-reproducing color picture tube.

The color television receiver also includes a three-beam color picture tube 13 serving as a color image-reproducing device such as a shadow mask color picture tube of the RCA type 19EY22 or ZlFJ P22 or 25AP22 A for example, The red, green and blue representative signals received from the receiver circuits 12 are impressed respectively upon electron guns 14, 15 and 16 of the tri-color picture tube 13. The three electron beams produced by these guns are deflected together over the target screen of the picture tube under the control of a deilection yoke 17. Also, the beams are maintained in convergence with each other by means of a suitably energized beam convergence yoke 18, an illustrative form of which will be described subsequently.

Also derived from the receiver circuits 12 are horizontal and vertical synchronizing signals which are impressed upon a synchronizing signal separator 19. The horizontal synchronizing signals are impressed upon the horizontal detlection circuit 21 and the vertical synchronizing signals are impressed upon the vertical detlection circuit 22. The horizontal and vertical deflection circuits are connected to the deilection yoke 17 as indicated by the reference characters HH and V-V. All of the apparatus of FIG- URE 1 described yup to this point may be of a conventional character.

Signals derived from the horizontal deilection circuit 21 at the horizontal deflection rate are impressed upon horizontal convergen-ce circuits 23, the output of which is connected to the electromagnets of the convergence yoke 18. Signals at the vertical deilection rate derived from the vertical deflection circuit 22 are impressed upon the vertical convergence circuits 24 for the production of suitable waves which also are impressed upon the electromagnets of the convergence yoke 18. Details of such vertical convergence circuits -by which suitable convergence waves are produced will be described subsequently. The horizontal convergence circuits are not part of the present invention and may be of a known type such as disclosed in Patent No. 2,903,622 granted Sept. 8, 1959 to J. C. Schopp.

Reference now is made to FIGURE 2 for a description of the physical relationship of the convergence electromagnets and the elec-tron beams controlled respectively D thereby as presently embodied in known commercial color television receivers.

This ligure is a transverse sectional view of the neck portion of a color picture tube as it appears when viewed from the luminescent screen end of the tube. The three electron beams 25 pass respectively between pairs of pole pieces 26, 27 and 28 located internally of the neck 29 of the picture tube 13. These pole pieces extend inwardly from the ends of substantially U-shaped cores of green, red and blue convergence electromagnets 3i), 31 and 32 respectively mounted externally around the neck of the picture tube. The convergence electromagnets are provided with horizontal frequency energizing windings designated 3BG, SSR and 33B and with vertical frequency energizing windings designated 34G, 341% and 34B respectively for the green, red and blue electromagnets 30, 31 and 32. Energization of the electromagnet windings produces a magnetic field between the corresponding pole pieces which moves the corresponding electron beam radially. There also may be included as part of the convergence electromagnet structure some means for effecting a static convergence of the electron beams 25. The static convergence means may be permanent magnets associated with the respective convergence electromagnets or may comprise windings on the respective electromagnets for energization by direct current of the proper amplitude and polarity to effect the desired static convergence of the electron beams. Such static convergence means is known and, since a description of it is not needed for an understanding of this invention, it is not shown.

Reference now is made to FIGURE 3 of the drawings. There is shown a vertical deflection output tube 35 having in its anode circuit a primary winding 36 of an output transformer 37. One of the secondary windings 33 of this transformer is coupled as indicated in the usual manner to the vertical windings of a deflection yoke (not shown) for deecting the three electron beams of the color picture tube to scan the luminescent screen of the picture ytube vertically at the rate of ap-proximately 60 elds per second. It is to be understood that horizontal windings of the yoke also will be energized to deflect the beams to scan the screen horizontally at the rate -of approximately 15,750 lines per second in the usual manner. The cathode circuit of the vertical output tube 35 includes a resistor 39 and a capacitor 40, connected between terminal 41 and ground and across which cathode circuit there is developed a voltage wave 42 at the vertical deflection frequency. The wave 42 has both sawtooth and parabolic components and iis of a particular character such that, when it is applied to the inductive energizing windings of the convergence electromagnets, it produces a generally parabolic current in these windings.

The cathode terminal 41 of the vertical output tube 35 is coupled by means including a series capacitor 43 and a resistive-capacitive wave-shaping shunt circuit 44 to the vertical frequency windings 34G, 34K and 34B respectively Vof the green, red and blue convergence electromagnets 3G, 31 and 32, respectively. The shunt circuit 44 serves to steepen the sides of the voltage wave 42 to produce a voltage wave 45. The impression of the voltage wave 45 upon the convergence apparatus causes an integration of this wave such that the green and red convergence electromagnet windings 34G and 34K are traversed by a substantially parabolic convergence current. The amplitude of the parabolic current for the green and `red Convergence electromagnet windings 34G and 34R respectively is controlled by a master amplitude control potentiometer 46, the movable contact of which is connected to terminal 47 to which also are connected the green and red electromagnet windings.

The vertical windings 34G and 34R of the green and red convergence electromagnets 30` and 31 respectively are connected in series to the movable contact of a master tilt control potentiometer' 48. the resistive element of which is connected across the terminals of another sccondary winding 49 4of the vertical detiection output transformer 37. A tap of this winding is grounded through a resistor 49C to provide a return path for the currents owing in the circuits including the windings of the convergence electromagnets. These currents develop a voltage wave 45a across the resistor 49e for a purpose to be later described. Pulse voltage Waves 50 and 51 of opposite polarity are developed respectively in the coils 49a and tf/b of the transformer winding and are available at the terminals of the winding. The impression of such pulses upon the convergence apparatus causes an integration of the pulses such that the convergence windings 34G and 34K are traversed by a substantially sawtooth current wave 52, the amplitude and polarity of which are determined by the adjustment of the master tilt control potentiometer 4S. The sawtooth current wave 52 is added to the generally parabolic current wave in the usual manner to tilt or phase the parabolic wave to effect substantial beam convergence at most points of the scanned raster.

A differential amplitude control potentiometer 53 has its resistive element connected across the series arrangement of the windings 34G and 34K of the green and red convergence electromagnets 30 and 31 respectively. The junction point 54 between the green and red windings 34G and 34K is connected to a tap of still another secondary winding 55 of the vertical deflection output transformer 37. Pulse voltage waves 50a and 51a of opposite polarity are developed respectively in the coils 55a and 5512 of this secondary winding and are available at the terminals of the winding. The terminals of this secondary winding 55 are connected to the terminals of t'ne resistive component of a diterential tilt control potentiometer 56. The movable contacts of the two differential potentiometers 53 and 56 are connected together. The adjustment of the movable contact of the differential amplitude control potentiometer 53 varies distribution of the parabolic current through the respective windings 34G and 34R of the green and red convergence electromagnets 30 and 31. The adjustment of the movable contact of the differential tilt control potentiometer 56 determines the distribution between the windings 3-tG and 34K of the green and red convergence electromagnets 30 and 31 of the sawtooth current wave 52 by controlling the combination with this wave of another sawtooth current wave resulting from the integration of voltage pulses 50a, 51a by the convergence apparatus.

The vertical frequency winding 34B of the blue convergence electromagnet 32 is energized by a substantially parabolic current wave, the amplitude and polarity of Which is adjusted by a blue control potentiometer 57 connected to terminal 58 in common with the winding 34B. This parabolic current wave is tilted or phased by means of a'suitable sawtooth component 52a, the amplitude and polarity of which are determined by the adjustment of a blue shape control potentiometer S9, the resistive element of which is connected across the terminals of the deection transformer secondary winding 49.

The green, red and blue convergence electromagnets 30, 31 and 32 also are provided with respective windings 33G, 33R and 33B as previously described and which are energized by suitably shaped waves at the horizontal deflection frequency. These windings may be energized by any suitable means such as that shown in Patent No. 2,903,622 granted Sept. 8, 1959, to I. C. Schopp.

The operation of the described beam convergence apparatus is virtually the same as that of similar apparatus previously used. In accordance with this invention, however, the circuits for energizing the green, red and blue convergence electromagnets 30, 31 and 32, respectively, at the vertical deflection rate, are different from the circuits previously used, because of the inclusion, therein, of tne terminating resistor 49C. While the inclusion of this circuit element does not alter the energization of the electromagnets, it does enable a greater adjustment tlcxibilty for the parabolic current wave to energize the Winding 3411 of the blue convergence electromagnet 32.

The voltage wave 45, which is impressed upon the windings 34G and 34R of the green and red electromagnets 3i) and 31, respectively, also is impressed upon the potentiometer 53, causing the development of the voltage wave 45a across the terminating resistor 49C. Because this terminating resistor represents only a portion of the total resistance in the described circuit, the wave 45a has a magnitude which is less than that of the wave 45. The general shape of the wave 45a is similar to that of the waves 45 and 45h, because, even though the parabolic current in the inductive windings 34G and 34R traverse the terminating resistor 49e, it also is traversed by current through the purely resistive circuit including the potentiometer 53, thereby having the same general shape as the voltage wave 45.

The circuit for energizing the winding 34b of the blue convergence electromagnet 32 includes the potentiometer 57 and also the terminating resistor 49C. It will be noted that, because of the series arrangement of the amplitude controlling potentiometers 46 and 57, the magnitude of the voltage wave 45b is less than that of the voltage wave 45. The magnitude of the wave 45h is determined by the adjustment of the potentiometer 57. With the movable contact of this potentiometer adjusted to the extreme ungrounded end of the resistor portion of the potentiometer, the wave 45b has its maximum amplitude which, by reason of the particular circuit design, is greater than the amplitude of the wave 45a produced across the terminating resistor 49C. It thus is seen that the voltage applied across the winding 34h of the blue electromagnet 32 is the difference between the voltages represented by the waves 4517 and 45a. With the potentiometer 57 adjusted as described to produce a maximum magnitude of the wave 45b, current ow through the winding 34b of the blue electromagnet 32 is, for example, from the lower to the upper terminals of this winding as viewed in the drawing.

As the movable contact of the potentiometer 57 is moved toward the grounded end of the resistor portion, the magnitude of the voltage wave 4511 decreases, thereby decreasing the amplitude of the current flowing through the blue electromagnet winding 34b. When a point is reached on the potentiometer 57 such that the magnitude of the voltage wave 45h is equal to the magnitude of the voltage wave 45a, there is no parabolic energizing current flowing through the blue electromagnet winding 34b. As the movable contact of the potentiometer 57 is moved further toward ground, the magnitude of the voltage wave 45b becomes less than that of the voltage wave 45a and thereby causes a current flow through the winding 34b which is, for example, from the upper to the lower terminals, thereof.

It is to be seen that, by reason of the inclusion of the terminating resistor 49C, it is possitble by means of the potentiometer 57 to change the direction of current flow through the blue electromagnet winding 341:. This has the desired effect of increasing the effectiveness of the potentiometer 57, thereby increasing the flexibility of the control of the blue electromagnet at the Vertical deflection rate.

What is claimed is:

1. In a color television image display system including a multiple beam color image reproducing device and deflection means for deecting said beams in a series of vertically spaced horizontal lines during successive beam trace periods to form a raster,

apparatus for converging said beams at all points of said raster comprising:

at least one dynamic convergence electromagnet having an energizing winding;

a source of a rst voltage wave of a particular character to produce a generally parabolic current wave in said one electromagnet energizing winding, said first voltage wave having a iirst maximum magnitude and a given polarity;

a source of a second voltage wave of said particular character and having said given polarity and a second magnitude less than said first maximum magnitude;

circuit means coupling the energizing winding of said electromagnet between said first and second voltage wave sources; and

control means for varying the magnitude of said first voltage wave from said maximum magnitude to a magnitude less than said second magnitude, whereby to effect a reversal of current flow in said electromagnet energizing winding, thus increasing the adjustment flexibility of said control means.

2. Beam converging apparatus in accordance with claim 1 and also including:

a second dynamic convergence electromagnet having an energizing winding;

a source of a third voltage wave of a character to produce a generally parabolic current wave in said second electromagnet energizing winding, said third voltage wave having said given polarity and a third magnitude greater than said rst maximum magnitude;

circuit means including a terminating impedance device coupling said third voltage wave source to the energizing winding of said second electromagnet;

said terminating impedance device functioning as said second voltage wave source.

3. Beam converging apparatus in accordance with claim 2 wherein:

said impedance device has a fixed value; and

said t-hird voltage wave source includes a iirst variable voltage device, whereby to alter the magnitudes of said second and third voltage waves.

4. Beam converging apparatus in accordance with claim 3 wherein:

said control means comprises a second variable voltage device, whereby to alter the magnitude of said first voltage wave from said first maximum magnitude to substantially zero.

5. Beam converging apparatus in accordance with claim 4 and also including:

a source of a substantially sawtooth voltage wave; and

means coupling said first and third parabolic voltage wave sources to said sawtooth wave source.

6. Beam converging apparatus in accordance with claim 5 wherein:

said impedance device comprises a fixed resistor; and

said first and second variable voltage devices respectively comprise irst and second potentiometers.

7. Beam converging apparatus in accordance with claim 6 wherein:

said first and second potentiometers are connected in series,

one terminal of said first potentiometer being coupled to said sawtooth voltage wave source, and

one terminal of said second potentiometer being connected to ground.

References Cited UNITED STATES PATENTS 3,114,858 12/1963 Schopp 315-22 3,258,643 6/1966 Lemke 315-22 RODNEY D. BENNETT, Primary Examiner. M. F. HUBLER, A ssstant Examiner. 

1. IN A COLOR TELEVISION IMAGE DISPLAY SYSTEM INCLUDING A MULTIPLE BEAM COLOR IMAGE REPRODUCING DEVICE AND DEFLECTION MEANS FOR DEFLECTING SAID BEAMS IN A SERIES OF VERTICALLY SPACED HORIZONTAL LINES DURING SUCCESSSIVE BEAM TRACE PERIODS TO FORM A RASTER, APPARATUS FOR CONVEYING SAID BEAM AT ALL POINTS OF SAID RASTER COMPRISING: AT LEAST ONE DYNAMIC CONVERGENCE ELECTROMAGNET HAVING AN ENERGIZING WINDING; A SOURCE OF A FIRST VOLTAGE WAVE OF A PARTICULAR CHARACTER TO PRODUCE A GENERALLY PARABOLIC CURRENT WAVE IN SAID ONE ELECTROMAGNET ENERGIZING WINDING, SAID FIRST VOLTAGE WAVE HAVING A FIRST MAXIMUM MAGNITUDE AND A GIVEN POLARITY; A SOURCE OF A SECOND VOLTAGE WAVE OF SAID PARTICULAR CHARACTER AND HAVING SAID GIVEN POLARITY AND A SECOND MAGNITUDE LESS THAN SAID FIRST MAXIMUM MAGNITUDE; CIRCUIT MEANS COUPLING THE ENERGIZING WINDING OF SAID ELECTROMAGNET BETWEEN SAID FIRST AND SECOND VOLTAGE WAVE SOURCES; AND CONTROL MEANS FOR VARYING THE MAGNITUDE OF SAID FIRST VOLTAGE WAVE FROM SAID MAXIMUM MAGNITUDE TO A MAGNITUDE LESS THAN SAID SECOND MAGNITUDE, WHEREBY TO EFFECT A REVERSAL OF CURRENT FLOW IN SAID ELECTROMAGNET ENERGIZING WINDING, THUS INCREASING THE ADJUSTMENT FLEXIBILITY OF SAID CONTROL MEANS. 